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United States Patent |
5,750,318
|
Lambert
,   et al.
|
May 12, 1998
|
Laser imaging element
Abstract
A laser-exposed thermal recording element comprising a support having
thereon a pigment layer comprising a pigment dispersed in a polymeric
binder, the pigment absorbing at the wavelength of a laser used to expose
the element, wherein the pigment comprises the formula:
Cu.sub.2-x M.sub.x (OH).sub.y R.sub.z :M'.sub.w
wherein:
M is at least one metal atom,
M' is at least one alkali metal,
R is at least one anion,
w is between 0 and 2,
x is between 0 and 1.5,
y and z are selected to maintain charge neutrality, with the proviso that
w, x and z cannot all be 0.
Inventors:
|
Lambert; Patrick M. (Rochester, NY);
Trauernicht; David P. (Rochester, NY);
Bringley; Joseph F. (Rochester, NY)
|
Assignee:
|
Eastman Kodak Company (Rochester, NY)
|
Appl. No.:
|
767054 |
Filed:
|
December 16, 1996 |
Current U.S. Class: |
430/346; 430/270.16; 430/495.1; 430/541; 430/616; 430/944; 430/964; 524/403; 524/406; 524/413 |
Intern'l Class: |
G03C 001/494; G03C 001/705; G03C 001/67; G03C 001/64 |
Field of Search: |
430/495.1,964,541,944,616,346,270.16
524/403,406,413
|
References Cited
U.S. Patent Documents
5489639 | Feb., 1996 | Faber et al. | 524/417.
|
Foreign Patent Documents |
4402329 | Aug., 1995 | DE.
| |
4028757-A | Jan., 1992 | JP.
| |
Primary Examiner: Schilling; Richard L.
Attorney, Agent or Firm: Cole; Harold E.
Claims
What is claimed is:
1. A laser-exposed thermal recording element comprising a support having
thereon a pigment layer comprising a pigment dispersed in a polymeric
binder, said pigment absorbing at the wavelength of a laser used to expose
said element, wherein said pigment comprises the formula:
Cu.sub.2-x M.sub.x (OH).sub.y R.sub.z :M'.sub.w
wherein:
M is at least one metal atom,
M' is at least one alkali metal,
R is a carboxylic acid salt, an amino acid salt,
an infrared-absorbing dye or iodate,
w is between 0 and 2,
x is between 0 and 1.5,
y and z are selected to maintain charge neutrality, with the proviso that
w, x and z cannot all be 0.
2. The element of claim 1 wherein M is nickel, cobalt, manganese,
magnesium, cerium, iron, zinc, silver or zirconium.
3. The element of claim 1 wherein M' is lithium, sodium or potassium.
4. The element of claim 1 wherein w is 0, x is 0, y is 3, z is 1, and R is
acetate, butyrate, propionate, isobutyrate or octanoate.
5. The element of claim 1 wherein w is 2, x is 0, y is 4, z is 0, and M' is
sodium.
6. The element of claim 1 wherein w is 0.5, x is 0, y is 4, z is 0, and M'
is lithium.
7. The element of claim 1 wherein w is 0, x is 0.2, y is 3, z is 1, M is
silver, and R is acetate.
8. The element of claim 1 wherein said pigment layer has an
infrared-absorbing material associated therewith.
9. The element of claim 1 wherein w is 0, x is 0, y is 3, z is 1, and R is
iodate.
10. A process of forming a single color image comprising
imagewise-exposing, by means of a laser, in the absence of a separate
receiving element, a thermal recording element comprising a support having
thereon a pigment layer comprising a pigment dispersed in a polymeric
binder, said pigment absorbing at the wavelength of a laser used to expose
said element, wherein said pigment comprises the formula:
Cu.sub.2-x M.sub.x (OH).sub.y R.sub.z :M'.sub.w
wherein:
M is at least one metal atom,
M' is at least one alkali metal,
R is a carboxylic acid salt, an amino acid salt, an infrared-absorbing dye
or iodate,
w is between 0 and 2,
x is between 0 and 1.5,
y and z are selected to maintain charge neutrality, with the proviso that
w, x and z cannot all be 0;
thereby providing said single color image.
11. The process of claim 10 wherein M is nickel, cobalt, manganese,
magnesium, cerium, iron, zinc, silver or zirconium.
12. The process of claim 10 wherein M' is lithium, sodium or potassium.
13. The process of claim 10 wherein w is 0, x is 0, y is 3, z is 1, and R
is acetate, butyrate, propionate, isobutyrate or octanoate.
14. The process of claim 10 wherein w is 2, x is 0, y is 4, z is 0, and M'
is sodium.
15. The process of claim 10 wherein w is 0.5, x is 0, y is 4, z is 0, and
M' is lithium.
16. The process of claim 10 wherein w is 0, x is 0.2, y is 3, z is 1, M is
silver, and R is acetate.
17. The process of claim 10 wherein said pigment layer has an
infrared-absorbing material associated therewith.
18. The process of claim 10 wherein w is 0, x is 0, y is 3, z is 1, and R
is iodate.
Description
This invention relates to laser imaging elements, and more particularly to
such elements which are used in medical imaging.
In recent years, thermal transfer systems have been developed to obtain
prints from pictures which have been generated electronically from a color
video camera. According to one way of obtaining such prints, an electronic
picture is first subjected to color separation by color filters. The
respective color-separated images are then converted into electrical
signals. These signals are then operated on to produce cyan, magenta and
yellow electrical signals. These signals are then transmitted to a thermal
printer. To obtain the print, a cyan, magenta or yellow dye-donor element
is placed face-to-face with a dye-receiving element. The two are then
inserted between a thermal printing head and a platen roller. A line-type
thermal printing head is used to apply heat from the back of the dye-donor
sheet. The thermal printing head has many heating elements and is heated
up sequentially in response to one of the cyan, magenta or yellow signals.
The process is then repeated for the other two colors. A color hard copy
is thus obtained which corresponds to the original picture viewed on a
screen. Further details of this process and an apparatus for carrying it
out are contained in U.S. Pat. No. 4,621,271, the disclosure of which is
hereby incorporated by reference.
Another way to thermally obtain a print using the electronic signals
described above is to use a laser instead of a thermal printing head. In
such a system, the donor sheet includes a material which strongly absorbs
at the wavelength of the laser. When the donor is irradiated, this
absorbing material converts light energy to thermal energy and transfers
the heat to the dye in the immediate vicinity, thereby heating the dye to
its vaporization temperature for transfer to the receiver. The absorbing
material may be present in a layer beneath the dye and/or it may be
admixed with the dye. The laser beam is modulated by electronic signals
which are representative of the shape and color of the original image, so
that each dye is heated to cause volatilization only in those areas in
which its presence is required on the receiver to reconstruct the color of
the original object. Further details of this process are found in GB
2,083,726A, the disclosure of which is hereby incorporated by reference.
Conventional silver halide laser imaging employs costly media and requires
a processing step. The latter requires the maintenance of a processor and
the accompanying chemistries for development and fixing, and the periodic
disposal of spent chemicals. Dry silver technologies (i.e., silver
behenate) require thermal development of an image, which may be obtained
using a laser, and the incorporation of a developing agent. The derived
images are conspicuous for their lack of stability. In laser ablation of
dye combinations, toxic decompositions are produced which must be
collected and disposed. All of the above technologies normally require
solvent coating of the media which have undesirable environmental
problems.
JP 4028757-A relates to an epoxy/resin composition suitable for writing by
laser-containing filler, e.g., zirconia, talc, etc., curing agent and
copper hydroxide which is changed to cupric oxide on heating with a laser.
This JP reference uses copper hydroxide which decomposes to give dark
images. However, in medical imaging, a significant emphasis is placed on
the throughput of images, i.e., how many images can be produced in a given
time period. This is directly proportional to the laser writing speed,
which is then correspondingly related to the thermal conversion
temperature of the imaging materials. The thermal conversion temperature
of copper hydroxide is high and limits the throughput of images. Further,
the images obtained have an undesirable brown tone.
DE 4402329 discloses the use of basic copper phosphate for laser-writable
coatings which give light-fast marks with high contrast when exposed with
an infrared or ultraviolet laser and allow one to produce colored images.
However, there is a problem with this material in that it has a high
conversion temperature, as will be shown hereafter.
U.S. Pat. No. 5,489,639 discloses a laser-markable thermoplastic
composition which contains a copper phosphate salt, copper sulfate, cupric
hydroxide phosphate or copper thiocyanate. However, there is a problem
with these materials in that they have a high conversion temperature, as
will be shown hereafter.
It is an object of this invention to provide a laser-imageable material
which has a faster throughput time than that of the prior art materials.
It is another object of the invention to provide a laser-imageable
material which does not have an undesirable brown tone upon imaging. It is
yet another object of this invention to provide a laser-imageable material
which has improved lightbox stability.
These and other objects are achieved in accordance with this invention
which relates to a laser-exposed thermal recording element comprising a
support having thereon a pigment layer comprising a pigment dispersed in a
polymeric binder, the pigment absorbing at the wavelength of a laser used
to expose the element, wherein the pigment comprises the formula:
Cu.sub.2-x M.sub.x (OH).sub.y R.sub.z :M'.sub.w
wherein:
M is at least one metal atom,
M' is at least one alkali metal,
R is at least one anion,
w is between 0 and 2,
x is between 0 and 1.5,
y and z are selected to maintain charge neutrality, with the proviso that
w, x and z cannot all be 0.
In a preferred embodiment of the invention, M is nickel, cobalt, manganese,
magnesium, cerium, iron, zinc, silver or zirconium. In another preferred
embodiment, M' is lithium, sodium or potassium. In still another preferred
embodiment, R is hydroxide, a carboxylic acid salt, an amino acid salt, an
infrared-absorbing dye or iodate. In yet still another preferred
embodiment, w is 0, x is 0, y is 3, z is 1, and R is acetate, butyrate,
propionate, isobutyrate or octanoate. In another preferred embodiment, w
is 2, x is 0, y is 4, z is 0, and M' is sodium. In yet still another
preferred embodiment, w is 0.5, x is 0, y is 4, z is 0, and M' is lithium.
In still another preferred embodiment, w is 0, x is 0.2, y is 3, z is 1, M
is silver, and R is acetate. In still another preferred embodiment, R is
an infrared-absorbing dye. In yet still another preferred embodiment, w is
0, x is 0, y is 3, z is 1, and R is iodate.
Another embodiment of the invention relates to a process of forming a
single color image comprising imagewise-exposing by means of a laser, in
the absence of a separate receiving element, a laser-exposed thermal
recording element as described above, thereby imagewise-heating the
pigment layer and causing it to change color, thereby creating the single
color image.
By use of the metal hydroxide-based compositions described in the
invention, the decomposition, or conversion temperatures, are lower than
the conversion temperatures of copper hydroxide described in the prior
art. A lower conversion temperature translates to a faster writing speed,
and hence, greater throughput. In addition, an image tone closely
resembling that of silver halide is obtained. Further, the imaging
elements of this invention can be conveniently coated out of a variety of
water-based polymers or gelatin.
Still further, the by-products of laser writing with the elements of this
invention are non-toxic, and are confined as integral components of the
coating. In addition, the Dmin tone of the unexposed media described
herein is consistent with accepted radiographic images.
Imaging with a compound, such as Cu(OH).sub.2, is accompanied by thermal
dehydration of the compound to yield the brown-to-black CuO composition.
The dehydration occurs above .about.175.degree. C., which is easily
obtained with exposure from commercially available red or IR lasers.
Improvements to the process would include a reduction in the thermal
energy required to achieve the dehydration or generate a black
decomposition product. This can be accomplished in several ways:
1) addition or inclusion of a metal salt (M') which accelerates the
dehydration or decomposition.
2) partial substitution of hydroxide by other ligands (R), or partial
substitution of Cu by other metals (M) yield a less stable hydroxide
composition that dehydrates at a lower temperature. By requiring less
energy for the dehydration, less energy needs to be deposited per unit
area. This translates directly to increased writing speed, and, higher
throughput.
3) partial substitution of hydroxide by other anions (R) which, through the
decomposition of the ligand, yield a dark product at a lower energy
density (e.g., R is an organic salt).
4) preheating, or predecomposing the metal hydroxide; thereby reducing the
amount of thermal energy required to complete the conversion to the black
oxide.
Alkali melt salts, such as lithium acetate, sodium acetate, and the
analogous hydroxides appear to accelerate the dehydration of Cu(OH).sub.2.
Another advantage of admixing alkali metal salts with the Cu(OH).sub.2 is
the tone of the exposed area is much closer to that accepted in medical
radiography. The blue black tone is contrasted to the brown black tone
generated from exposing Cu(OH).sub.2 without the presence of an alkali
metal salt.
Basic copper acetate, Cu.sub.2 (OH).sub.3 (OAc), is a preferred composition
of this invention because of its lower conversion, or darkening,
temperature compared to Cu(OH).sub.2. Correspondingly, coatings that
contain the basic acetate show faster writing speeds than Cu(OH).sub.2
coatings. X-ray powder diffraction analysis shows that the basic acetate
structure is still present to a significant degree in the dark
decomposition product. This suggests that the basic acetate structure may
be less stable than that of Cu(OH).sub.2, and the incomplete combustion of
the acetate anion during decomposition may be the source of a carbon-rich
pigmenting byproduct. Note that the basic copper acetate structure is
unique and is not an obvious extension of the Cu(OH).sub.2 structure.
The basic copper acetate structure lends itself to the synthesis of several
additional compositions of this invention. The compound possesses a
layered structure with corrugated sheets of Cu--OH(OAc) coordination
spheres. The acetate anions bridge between adjacent sheets. A novel
characteristic of this host compound is the ability to exchange the
acetate anions for long chain carboxylates, amino acids, organic sulfates,
inorganic anions such as IO.sub.4.sup.-, S.sup.-2, and S.sub.2
O.sub.3.sup.-2. Uncharged species such as NH.sub.3 are also anticipated.
The preparation of the exchanged materials usually requires stirring the
basic copper acetate in a .about.1M solution containing the dissolved
anion of choice.
Some of these materials exhibit lower conversion temperatures than that of
the basic copper acetate compound, and several have conversion
temperatures below Cu(OH).sub.2. The body color of the exchanged compounds
is often bluer than the blue-green color of the basic copper acetate. This
allows one to optimize the Dmin tone in a coating. Note, as described
above for the case of Cu(OH).sub.2, the use of alkali metal salts also
enhances the writing speed for coatings containing basic copper acetate.
Another novel feature is the ability to exchange IR-absorbing dyes into the
basic copper acetate structure. Such an intimate association of the laser
absorbing dye has obvious implications for rapid heat transfer to the
imaging element.
Furthermore, several different metal cations from across the periodic table
can be incorporated into the structures of the materials described above,
without any reduction in conversion temperature or writing speed. A
reduction in conversion temperature and an increase in writing speed are
realized with Ag substitution.
The metal hydroxide composition may also be preheated prior to dispersion
in such a manner that the light body color is retained, and dehydration is
initiated. Less thermal energy is required to complete the conversion to
the final dark decomposition product, thus, a faster writing speed is
realized.
Finally, many of the copper salts described herein are conveniently
precipitated, crystallized or exchanged within a gelatin or polymer
solution, allowing designed particle size, coatability and homogeneity.
In general, the particle size of the pigment employed in the invention
should be between 0.05-10 .mu.m and the pigment-to-binder weight ratio
should be between 0.25 and 5.0. In a preferred embodiment of the
invention, the pigment is present in an amount of from about 0.01
g/m.sup.2 to about 0.500 g/m.sup.2 of the element.
Examples of pigments useful in the invention include the following:
______________________________________
Cu.sub.2-x M.sub.x (OH).sub.y R.sub.z :M'.sub.w
M x M' w y R z
______________________________________
NA* 0 Na 2 4 NA* 0
NA* 0 Li 0.5 4 NA* 0
NA* 0 NA* 0 3 acetate 1
NA* 0 NA* 0 3 butyrate 1
NA* 0 NA* 0 3 propionate
1
NA* 0 NA* 0 3 isobutyrate
1
NA* 0 NA* 0 3 octanoate
1
NA* 0 NA* 0 3 glycine 1
NA* 0 NA* 0 3 l-aspartic
1
NA* 0 NA* 0 3 iodate 1
Ag 0.2 NA* 0 3 acetate 1
Fe 0.02 NA* 0 3 acetate 1
Zr 0.02 NA* 0 3 acetate 1
Ce 0.02 NA* 0 3 acetate 1
Ni 0.2 NA* 0 3 acetate 1
Mg 0.5 NA* 0 3 acetate 1
Zn 1.0 NA* 0 3 acetate 1
Co 1.75 NA* 0 3 acetate 1
______________________________________
*NA-not applicable
The pigment layer of the recording element of the invention may also
contain an ultraviolet-absorbing dye, such as a benzotriazole, a
substituted dicyanobutadiene, an aminodicyanobutadiene, or materials such
as those disclosed in Patent Publications JP 58/62651; JP 57/38896; JP
57/132154; JP 61/109049; JP 58/17450; or DE 3,139,156, the disclosures of
which are hereby incorporated by reference. They may be used in an amount
of from about 0.05 to about 10 g/m.sup.2.
The recording elements of this invention can be used to obtain medical
images, reprographic masks, printing masks, etc. The image obtained can be
a positive or a negative image. The process of the invention can generate
either continuous (photographic-like) or halftone images.
The invention is especially useful in making reprographic masks which are
used in publishing and in the generation of printed circuit boards. The
masks are placed over a photosensitive material, such as a printing plate,
and exposed to a light source. The photosensitive material usually is
activated only by certain wavelengths. For example, the photosensitive
material can be a polymer which is crosslinked or hardened upon exposure
to ultraviolet or blue light, but is not affected by red or green light.
For these photosensitive materials, the mask, which is used to block light
during exposure, must absorb all wavelengths which activate the
photosensitive material in the Dmax regions and absorb little in the Dmin
regions. For printing plates, it is therefore important that the mask have
high blue and UV Dmax. If it does not do this, the printing plate would
not be developable to give regions which take up ink and regions which do
not.
By use of this invention, a mask can be obtained which has enhanced
stability to light for making multiple printing plates or circuit boards
without mask degradation.
Any polymeric material may be used as the binder in the recording element
employed in the invention. For example, there may be used cellulosic
derivatives, e.g., cellulose nitrate, cellulose acetate hydrogen
phthalate, cellulose acetate, cellulose acetate propionate, cellulose
acetate butyrate, cellulose triacetate, a hydroxypropyl cellulose ether,
an ethyl cellulose ether, etc.; gelatin; polycarbonates; polyurethanes;
polyesters; poly(vinyl acetate); polystyrene;
poly(styrene-co-acrylonitrile); a polysulfone; a poly(phenylene oxide); a
poly(ethylene oxide); a poly(vinyl alcohol-co-acetal) such as poly(vinyl
acetal), poly(vinyl alcohol-co-butyral) or poly(vinyl benzal); or mixtures
or copolymers thereof. The binder may be used at a coverage of from about
0.1 to about 5 g/m.sup.2.
A barrier layer may be employed in the laser recording element of the
invention if desired, as described in U.S. Pat. No. 5,459,017, the
disclosure of which is hereby incorporated by reference.
To obtain a laser-induced image according to the invention, an infrared
diode laser is preferably employed since it offers substantial advantages
in terms of its small size, low cost, stability, reliability, ruggedness,
and ease of modulation.
The pigment layer of the recording element of the invention may also have
associated therewith an infrared-absorbing material such as cyanine
infrared-absorbing dyes as described in U.S. Pat. No. 4,973,572, or other
materials as described in the following U.S. Pat. Nos.: 4,948,777;
4,950,640; 4,950,639; 4,948,776; 4,948,778; 4,942,141; 4,952,552;
5,036,040; and 4,912,083, the disclosures of which are hereby incorporated
by reference. The infrared-absorbing material may be either in the pigment
layer or a layer underneath or on top thereof. The laser radiation is then
absorbed into the recording layer and converted to heat by a molecular
process known as internal conversion. As used herein, an
infrared-absorbing dye has substantial light absorptivity in the range
between about 700 nm and about 1200 nm.
Lasers which can be used in the invention are available commercially. There
can be employed, for example, Laser Model SDL-2420-H2 from Spectra Diode
Labs, or Laser Model SLD 304 V/W from Sony Corp. In addition, other
methods for applying thermal energy to the recording elements of the
invention may be used such as thermal prints heads.
Any material can be used as the support for the recording element of the
invention provided it is dimensionally stable and can withstand the heat
of the laser. Such materials include polyesters such as poly(ethylene
naphthalate); polysulfones; poly(ethylene terephthalate); polyamides;
polycarbonates; cellulose esters such as cellulose acetate; fluorine
polymers such as poly(vinylidene fluoride) or
poly(tetrafluoroethylene-co-hexafluoropropylene); polyethers such as
polyoxymethylene; polyacetals; polyolefins such as polystyrene,
polyethylene, polypropylene or methylpentene polymers; and polyimides such
as polyimideamides and polyether-imides. The support generally has a
thickness of from about 5 to about 200 .mu.m.
A thermal printer which uses a laser as described above to form an image on
a thermal print medium is described and claimed in U.S. Pat. No.
5,168,288, the disclosure of which is hereby incorporated by reference.
Image dyes could also be added to the recording layer of the invention such
as those dyes disclosed in U.S. Pat. Nos. 4,541,830; 4,698,651; 4,695,287;
4,701,439; 4,757,046; 4,743,582; 4,769,360; and 4,753,922, the disclosures
of which are hereby incorporated by reference.
EXAMPLES
The following examples are provided to illustrate the invention.
All of the chemicals used in the following examples are of reagent grade
unless otherwise specified. Hydration numbers for starting materials and
products are approximate or undetermined, with no implications to the
formula above. Also, stoichiometries and ion charges should not be
considered definitive, but rather, approximate, as deduced from
established chemistry.
The coated samples were evaluated on a drum scanner system consisting of a
13 cm diameter drum which was 25 cm long. The samples were mounted on the
outside surface of the drum. The rotational speed of the drum could be
varied from 1-800 rev/min. A diode laser (827 nm) was aimed perpendicular
to the drum surface, and was focussed to a 6.mu..times.8.mu. 1/e.sup.2
full width spot at the sample surface. The laser power could be varied
from 0-100 mW. The pitch of the scan was 5.mu. for all rotational speeds.
The focal position of the laser was adjusted to accommodate the different
substrate thickness. Writing speed was determined by two methods, or the
combination of these methods; 1) comparison of the rotational speed
required to give equivalent optical density in the exposed areas (higher
rev/min indicates faster writing speed); and/or 2) comparison of optical
density in exposed areas written at the same rotational speed (higher
optical density indicates faster writing speed).
The anticipated writing speed in a coating of a material was approximated
by the "conversion" temperature of the material. The compound was loaded
into a melting point capillary, and observed in the oil bath of a melting
point unit as the temperature was increased. With the same rate of
temperature increase, the conversion temperature is considered as the
midpoint of the temperature range where the compound changed color to a
brown-black or black tone. Optical densities were measured on a
transmission densitometer (X-rite, Inc.).
Example 1
Copper Hydroxide and Basic Copper Acetate Writing Speeds
This example compares the writing speeds of a Cu(OH).sub.2 (x=0, y=4)
coating and a basic copper acetate (x=0, y=3, R=acetate, z=1) coating.
Control C1:
Copper hydroxide, Cu(OH).sub.2, was prepared by the precipitation of a
.about.0.5M CuCl.sub.2 solution with a 5 wt % aqueous NaOH solution at
25.degree. C. The amorphous blue precipitate was collected by vacuum
filtration and washed with copious amounts of water, until free of
Na.sup.+ ion. The collected material was air dried.
A copper hydroxide dispersion was prepared by the combination of 3.00 g of
Cu(OH).sub.2, 9.24 g of a 13 wt % solution of Permuthane (ICI) dissolved
in 93:7 (w/w) methylene chloride/methanol, 55.0 g of 93:7 (w/w) methylene
chloride/methanol and 165 g of 0.3 cm ceramic milling beads in a 125 ml
plastic bottle. The dispersion was milled until the average particle size
was 1-2.mu., and was then coated using a 125 m.mu. doctor blade on a clear
175 m.mu. Estar.RTM. plastic support. The writing speed was 30 rev/min.
Invention E1:
Basic copper acetate was prepared as follows: 3.0 g of Cu(acetate).sub.2
H.sub.2 O was dissolved in 160 ml of distilled H.sub.2 O. A dilute NaOH
solution (0.902 g NaOH in 40 ml of distilled water) was slowly added to
the stirred solution. The bright blue-green precipitate was collected by
vacuum filtration, washed with 1 L of distilled water and air-dried.
A basic copper acetate dispersion was prepared by combining 2.79 g of
Cu.sub.2 (OH).sub.3 (OAc), 8.55 g of a 13 wt % solution of Permuthane
(ICI) dissolved in 93:7 (w/w) methylene chloride/methanol, 45.2 g of 93:7
(w/w) methylene chloride/methanol and 165 g of 0.3 cm ceramic milling
beads in a 125 ml plastic bottle. The dispersion was milled until the
average particle size was 1-2.mu., and was then coated using a 125 m.mu.
doctor blade on a clear 175 m.mu. Estar.RTM. plastic support. The writing
speed was 60 rev/min.
The basic copper acetate coating of the invention exhibits significantly
faster writing speed than that of the prior art Cu(OH).sub.2 coating.
To verify the correlation of conversion temperature to writing speed, the
conversion temperatures of powders used in C1 and E1 were measured. The
Cu(OH).sub.2 had a conversion temperature range of 170.degree.-175.degree.
C., while the basic copper acetate of the invention has a conversion
temperature range of 135.degree.-145.degree. C. The above data show that
the invention elements have lower conversion temperatures.
Example 2
Alkali Metal (M'=Sodium) Salt Effect on Writing Speed
This example demonstrates the effect of mixing an alkali metal salt, in
this case, sodium acetate, with Cu(OH).sub.2.
For C2 and E2-E4 a source dispersion was prepared by dissolving 4.40 g of
gelatin (Eastman Kodak) in warm distilled water, followed by the addition
of 10 g of Cu(OH).sub.2 (prepared as in C1). The mixture was transferred
to a 500 ml plastic bottle containing 550 g of 0.3 cm ceramic milling
beads. 0.33 ml of antifoam-289 (Sigma) was added and the dispersion
ball-milled for 7 days. The final particle size of the copper hydroxide
was 1-2.mu..
Control C2:
0.33 ml of gelatin hardener (HAR-2088, Eastman Kodak Co.) and 0.065 ml of
Triton-Xa 100 surfactant was added to a 15 ml aliquot of the source
dispersion. This mixture was then coated on a clear, gelatin-subbed, Estar
plastic support using a 125 m.mu. doctor blade at a coating block
temperature of 10.degree.-15.degree. C.
Invention E2:
The preparation was identical to that of Control C2, except for the
addition of 0.34 ml of a sodium acetate solution to the dispersion
immediately after the addition of the surfactant. This gave a ›Na!/›Cu!
molar ratio of 0.1 (w is 0.2).
Invention E3:
Same as E2, except that 1.70 ml of the sodium acetate solution was added.
This gave a ›Na!/›Cu! molar ratio of 0.5 (w is 1.0).
Invention E4:
Same as E2, except that 3.40 ml of the sodium acetate solution was added.
This gave a ›Na!/›Cu! molar ratio of 1.0 (w is 2).
The above coatings were printed as above at two different writing speeds.
The optical density was evaluated qualitatively for the darkness of the
mark as follows: no mark, slight mark, heavy mark and very heavy mark. The
following results were obtained:
TABLE 1
______________________________________
Effect on Na.sub.w on writing speed of copper hydroxide coatings
Example w 30 rev/min 60 rev/min
______________________________________
C2 (Control)
0 slight mark no mark
E2 0.2 slight mark no mark
E3 1.0 heavy mark slight mark
E4 2.0 very heavy mark
slight mark
______________________________________
As can be seen from the above table, as the sodium level increases, the
optical density in the exposed areas increases (mark intensity increases),
thus indicating an increase in writing speed.
Example 3
Alkali Metal Salt (M'=Lithium) Effect on Writing Speed
This example demonstrates the effect of mixing an alkali metal salt, in
this case, lithium acetate, with Cu(OH).sub.2. The difference in writing
speed is indicated by an increase in the optical density of lines written
at the same rotational speed.
Crystalline Cu(OH).sub.2 was prepared by first dissolving 99.872 g of
CuSO.sub.4.5H.sub.2 O in 800 ml of hot (70.degree. C.) distilled water
followed by the dropwise addition of 86 ml of 6M NH.sub.4 OH to yield the
basic sulfate salt. The green precipitate was collected by vacuum
filtration and washed 4X with 200 ml of hot distilled water. The moist
cake was then triturated with 300 ml of a 5 wt % NaOH solution. The blue
Cu(OH).sub.2 was collected and washed as above. The crystalline
Cu(OH).sub.2 x-ray pattern was verified by powder diffractometry.
Control C3:
Very fine (<1.mu.) Cu(OH).sub.2 was prepared by dissolving 6 g of the
Cu(OH).sub.2 prepared above in 600 ml of 12M NH.sub.4 OH, followed by the
rapid addition of 300 ml of acetone. The milky blue-white precipitate was
collected by vacuum filtration and dried in air. One gram of this material
was combined with 0.4 g of Permuthane.RTM. (ICI PLC) binder, and 99 g of
methylene chloride/methanol (93/7) solvent in a 4 dram vial. One and a
half g of 2 mm glass beads were added and the sealed vial agitated on a
paint shaker for 1 hour. The dispersion was coated with a 75 m.mu. blade
on 175 m.mu. subbed Estar.RTM.. The coating exhibited a weak line when
written at 60 rev/min. The difference in optical density between written
and unwritten regions at this rotational speed was 0.075.
Invention E5:
Fine particle Cu(OH).sub.2 from C3 was treated with 25 mol %
Li(CH3CO2).2H.sub.2 O methanolic solution. The sample was air dried with
stirring. 1 gram of this material was combined with 0.4 g of
Permuthane.RTM. binder, and 99 g of methylene chloride/methanol (93/7)
solvent in a 4 dram vial. 1.5 g of 2 mm glass beads were added and the
sealed vial agitated on a paint shaker for 1 hour. The dispersion was
coated with a 75 m.mu. blade on 175 m.mu. subbed Estar.RTM.. An easily
observable line was written at 60 rev/min. The difference in optical
density between written and unwritten regions of this coating was 0.415.
The above results show that an increase in optical density is obtained if
lithium is present. This translates to an increase in writing speed.
Example 4
Metal Substitution into Basic Copper Acetate (R=OAc, M=Ag)
Comparison C4:
10 g of copper acetate monohydrate was dissolved in 600 ml of distilled
water. A dilute NaOH solution (3.15 g in 200 ml) was added dropwise into
the stirred solution. After addition, the blue-green precipitate was
collected by vacuum filtration and washed with 500 ml of distilled water.
Invention E6:
10 g of copper acetate monohydrate and 0.418 g of silver acetate (x=0.1)
were dissolved in 600 ml of distilled water. A dilute NaOH solution (3.15
g in 200 ml) was added dropwise into the stirred solution. After addition,
the blue-green precipitate was collected by vacuum filtration and washed
with 500 ml of distilled water.
Invention E7:
10 g of copper acetate monohydrate and 0.835 g of silver acetate (x=0.2)
were dissolved in 600 ml of distilled water. A dilute NaOH solution (3.3 g
in 200 ml) was added dropwise into the stirred solution. After addition,
the blue-green precipitate was collected by vacuum filtration and washed
with 500 ml of distilled water.
Coatings of these materials were prepared in gelatin (Eastman Kodak) at a
P/B ratio of 2.5:1 in a similar manner to the above examples.
The conversion temperatures of the powders and the writing speeds of the
coatings are shown below in Table 2:
TABLE 2
______________________________________
Writing speeds and conversion temperatures for M = Ag; R = OAc
Conversion
Temperature
Example x (.degree.C.)
Writing Speed
______________________________________
C4 (Comparison)
0 140-145 60
E6 0.1 130-135 90
E7 0.2 115-120 90
______________________________________
The above results again demonstrate the correspondence between conversion
temperature and writing speed. The addition of Ag to the inventive basic
copper acetate lowers the conversion temperature and increases the writing
speed.
Example 5
Exchanged Dye in Basic Copper Acetate (R=OAc, Dye)
Cu.sub.2 (OH).sub.3 (OAc) is a layered compound having sheet-like
arrangements of Cu.sup.2+ and OH.sup.- ions separated and linked by
acetate layers. This example shows that among the various charged
molecules that can be intercalated or exchanged into the layered structure
of Cu.sub.2 (OH).sub.3 (OAc), IR-absorbing dyes are particularly
effective.
Comparison C5:
A basic copper acetate dispersion was prepared by the combination of 1.00 g
of Cu.sub.2 (OH).sub.3 (OAc) (see above for preparation), 3.08 g of a 13
wt % solution of Permuthane (ICI) binder dissolved in 93:7 (w/w) methylene
chloride/methanol, 25.0 g of 93:7 (w/w) methylene chloride/methanol and 75
g of 0.3 cm ceramic milling beads in a 100 ml glass bottle. The dispersion
was milled until the average particle size was 1-2.mu., and was then
coated using a 125 m.mu. doctor blade on a clear 175 m.mu. Estar.RTM.
plastic support. The writing speed was 60 rev/min.
Invention E8:
0.050 g of an anionic enamine tricarbocyanine IR-absorbing dye was
dissolved in 25 ml of methanol, and then added to a 1.00 g suspension of
Cu.sub.2 (OH).sub.3 (OAc) in 25 ml of distilled water with stirring. The
suspension was stirred for 5 hours and then the solid collected by vacuum
filtration. The filtrate was clear and colorless, indicating that the
laser dye had been completely intercalated, or exchanged, into the copper
basic acetate host. The solid was allowed to air dry, and then was coated
as shown for Control C3. The writing speed was 240 rev/min.
The above results show that the exchange of charged IR-absorbing dyes for
the carboxylate groups of the basic copper carboxylates dramatically
improves the writing speed of the resulting medium.
Example 6
Conversion Temperature and Writing Speed for Basic Copper Butyrate (x=0,
y=3, z=1, R=Butyrate)
Invention E9:
The basic copper butyrate compound was prepared by stirring 1.00 g of basic
copper acetate in a dilute solution of sodium butyrate. The conversion
temperature of this compound was found to be 115.degree.-120.degree. C. 1
g of this material was combined into a 4 dram glass vial with 0.4 g of
poly(methyl methacrylate) binder in 5 g acetone. 1.5 g of 2 mm glass beads
were added as media, and the mixture shaken for a hour on a paint shaker.
The dispersion (light blue) was coated on 175 m.mu. clear estar support
with a 75 m.mu. blade. The coating was written upon easily at 60 rev/min
with a faint mark observed at 120 rev/min. The results are summarized in
Table 3 below with C1 as as control:
TABLE 3
______________________________________
Basic copper butyrate results
Conversion
Temperature 60 rev/min
Example (.degree.C.) Writing Speed
.DELTA.OD
______________________________________
C1 170-175 30 0.075
E9 115-120 120 0.62
______________________________________
The above results show that a fourfold increase in writing speed is
obtained using basic copper butyrate as compared to the Cu(OH).sub.2
coating described in C1, as would be expected from the differences in
conversion temperature. This increase in performance is also indicated by
the change in optical density upon writing at 60 rev/min.
Example 7
Other Exchanged Basic Copper Compounds (R=Carboxylate)
Other basic copper salts (E10, E11, E12 and C6) were formed by mixing
aqueous solutions of the sodium salts of the carboxylic acids, or dilute
solutions of the carboxylic acids with a small amount (0.25-1.00 g) of
copper basic acetate, Cu.sub.2 (OH).sub.3 (OAc), prepared as described
above. It was assumed that the excess of exchange anion ensured complete
substitution. Some samples were examined with x-ray powder diffraction to
verify the change in the basal plane distance of the layered basic copper
carboxylate structure from that of the basic acetate. Below, in Table 4,
the conversion temperatures of several of these materials are compiled
(including the R=acetate and butyrate examples previously described):
TABLE 4
______________________________________
R = Carboxylic acid anions
Conversion
Example Exchange Anion
Color Temperature
______________________________________
E1 acetate green 135-145.degree. C.
E9 butyrate blue 115-120.degree. C.
E10 propionate blue 115-127.degree. C.
E11 isobutyrate light green
163-168.degree. C.
E12 octanoate blue-green 105-115.degree. C.
C6 (control)
formate light green
>200.degree. C.
______________________________________
The above results show that the conversion temperature decreases with
increases in the length of the carbon chain in the carboxylic acid. Based
on the coating control shown in E9 above, this reduction will correspond
to an increase in writing speed. All of these materials exhibited
conversion temperatures lower than that of Cu(OH).sub.2. The basic formate
composition of C6 is an example of an exchanged material with a
decomposition temperature higher than that of Cu(OH).sub.2.
Example 8
Amino Acid Exchange in Basic Copper Acetate
Amino acids can be exchanged into the copper basic acetate structure
similarly to the carboxylic acid examples described above.
Invention E13:
0.25 g of copper basic acetate (prepared as above) was added to a 0.1M
solution of the sodium salt of glycine, NaCO.sub.2 CH.sub.2
NH.sub.2.nH.sub.2 O. After 45 minutes of stirring, the exchanged material
was collected by vacuum filtration and air dried. The conversion
temperature was 135.degree.-142.degree. C.
Invention E14:
0.25 g of copper basic acetate (prepared as above) was added to a 0.1M
solution of the potassium salt of L-aspartic acid KCO.sub.2 NH.sub.2
CHCH.sub.2 CO.sub.2.nH.sub.2 O. After 3 hours of stirring, the exchanged
material was collected by vacuum filtration and air dried. The conversion
temperature was 150.degree.-155.degree. C.
The data show that the basic amino acid copper salts (R=amino acid) have a
lower conversion temperature than that of the prior art Cu(OH).sub.2, and
thus would result in faster writing speeds.
Example 9
Inorganic Anion Exchange into Basic Copper Acetate (R=IO.sub.4.sup.-)
Invention E15:
0.25 g of basic copper acetate was stirred into a 0.5 M solution of
NaIO.sub.4, let stand overnight, and then collected by vacuum filtration.
The green compound had a conversion temperature of 150.degree. C.
The example demonstrates that the substitution of inorganic anions for
hydroxide can yield materials which have lower conversion temperatures
than that of Cu(OH).sub.2, C1.
Example 10
The examples below show that a wide range of metal cations can be
substituted into the basic copper acetate composition without negatively
impacting the inventive qualities. The universal aspect of M substitution
will be described through the range of x=1.75 with examples of different
cations (Fe, Zr, Ce, Ni, Mg, Zn, Co).
Iron into Basic Copper Acetate (x=0.02)
Invention E16:
13.00 g of Cu(OAc).sub.2.H.sub.2 O was dissolved in 200 ml of distilled
water along with 0.18 g of Fe(SO.sub.4).7H.sub.2 O. The solution was
brought to pH .about.7 with the dropwise addition of 11 ml of 6M NH.sub.4
OH. After stirring for 1.5 hours the blue green product was collected by
vacuum filtration and air-dried. The conversion temperature of this
material was 135.degree.-140.degree. C.
Zr.sup.4+ into Basic Copper Acetate (x=0.02)
Invention E17:
6.5 g of Cu(OAc).sub.2.H.sub.2 O was dissolved in 100 ml of distilled
water, followed by the addition and dissolution of 0.105 g of
ZrOCl.sub.2.8H.sub.2 O (Teledyne Wah Chang Albany, RGS). 5 wt % NaOH was
added dropwise to this solution until a pH of 7.5 was reached. The blue
precipitate was collected by vacuum filtration and air dried. The
conversion temperature was 143.degree.-147.degree. C.
Ce.sup.4+ into Basic Copper Acetate (x=0.02)
Invention E18:
19.967 g of Cu(OAc).sub.2.H.sub.2 O and 0.548 g of (NH.sub.4).sub.2
Ce(NO.sub.3).sub.6.nH.sub.2 O (REacton) were dissolved in 500 ml of
distilled water. 250 ml of 0.4M NaOH solution was added dropwise. The
precipitated solution was stirred 1 hour and then collected by vacuum
filtration, and air dried. The conversion temperature of the blue green
precipitate was 146.degree.-153.degree. C.
Ni.sup.2+ into Basic Copper Acetate (x=0.2)
Invention E19:
5.850 g of Cu(OAc).sub.2.H.sub.2 O and 0.811 g of Ni(OAc).sub.2.4H.sub.2 O
were dissolved in 150 ml of distilled water. 25 ml of 5 wt % NaOH was
added dropwise to the solution. The precipitated solution was stirred
overnight and then collected by vacuum filtration, and air dried. The
conversion temperature of the blue green precipitate was
147.degree.-160.degree. C.
Mg.sup.2+ into Basic Copper Acetate (x=0.5)
Invention E20:
4.874 g of Cu(OAc).sub.2.H.sub.2 O and 1.745 g of Mg(OAc).sub.2.4H.sub.2 O
were dissolved in 150 ml of distilled water. 25 ml of 5 wt % NaOH was
added dropwise to the solution. The precipitated solution was stirred
overnight and then collected by vacuum filtration, and air dried. The
conversion temperature of the light blue precipitate was
130.degree.-142.degree. C.
Zn.sup.2+ into Basic Copper Acetate (x=1.0)
Invention E21:
5.989 g of Cu(OAc).sub.2.H.sub.2 O and 6.585 g of Zn(OAc).sub.2.2H.sub.2 O
were dissolved in 200 ml of distilled water and brought to pH .about.7
with 5 ml of 6M NH.sub.4 OH. The precipitate was stirred for 1 hour and
collected by vacuum filtration. X-ray powder diffraction indicated the
incorporation of Zn.sup.2+. The air dried material had a conversion
temperature of 135.degree.-155.degree. C.
Co.sup.2+ into Basic Copper Acetate (x=1.75)
Invention E22:
16.556 g of Co(NO.sub.3).sub.2.6H.sub.2 O was dissolved in 200 ml of
distilled water, along with 1.963 g of Cu(NO.sub.3).sub.2.3H.sub.2 O. 3.5
ml of concentrated NH.sub.4 OH was added dropwise. The gray-green
precipitate was collected and dried. 0.25 g of this material was exchanged
in 100 ml of a 1.0M NaCH.sub.3 CO.sub.2 solution for three hours with
stirring. The decomposition temperature of the composition (nominally
Co.sub.3.5 Cu.sub.0.5 (OH).sub.6 (OAc).sub.2.nH.sub.2 O) was
135.degree.-175.degree. C.
The above materials all have conversion temperatures lower than that of
Cu(OH).sub.2, C1.
Example 11
The following examples are controls with the other copper salts cited in
the prior art as laser-imaging elements:
Copper Basic Phosphate, Cu.sub.4 (OH).sub.2 (PO.sub.4).sub.2 -C7
This material is described in DE 440 2329. Examination of commercial copper
basic phosphate did not show a conversion temperature up to 250.degree. C.
Therefore, this material was made by first dissolving 2.5 g of
CuSO.sub.4.5H.sub.2 O in 20 ml of distilled water and 3.8 g of Na.sub.3
PO.sub.4.12H.sub.2 O in 40 ml of distilled water. The copper solution was
added directly to the phosphate solution with stirring. The sample was
collected by vacuum filtration and air dried. The conversion temperature
of the material was measured as >200.degree. C.
Thus the prior art copper basic phosphate had a conversion temperature much
higher than the conversion temperature of the materials of the invention.
Example 12
Described below are processes for the production of the imaging elements
described herein.
In Situ Preparation of Basic Copper Salts
Invention E23:
The basic acetate can be prepared directly in a gelatin base for convenient
dispersion, coating, and particle size control. For example, 6 g of
Cu(OAc).sub.2.2H.sub.2 O and 10 g of gelatin (Class 32-Type IV, Eastman
Kodak) were added to 120 ml of water. The melt was complete after heating
at 60.degree. C. 6M NH.sub.4 OH was added dropwise to the stirring melt
until a neutral pH was achieved. Crystals of 2-10.mu. dimensions were
observed at this point. The crystals were isolated via cold water dilution
of the melt. X-ray powder diffraction of the crystals showed the pattern
of basic copper acetate.
Several of the basic copper salts described previously are amenable to
preparation via this route. The advantages include particle size control,
ease of dispersion and homogeneity
Preheating Cu(OH).sub.2 to Increase Writing Speed
Invention E24:
Fine particle Cu(OH).sub.2 from C3 was treated at 120.degree. C. for 1/2
hour. 1 gram of this material was combined with 0.4 g of Permuthane.RTM.
binder, and 99 g of methylene chloride/methanol (93/7) solvent mixture in
a 4 dram vial. 1.5 g of 2 mm glass beads were added and the sealed vial
agitated on a paint shaker for 1 hour. The dispersion was coated with a 75
m.mu. blade on 175 m.mu. subbed Estar.RTM.. An easily observable line was
written at 60 rev/min. The difference in optical density between written
and unwritten regions of this coating was 0.205 compared with 0.075 for
the Cu(OH).sub.2 in C3.
The above results show that an increase in optical density is obtained if
the Cu(OH).sub.2 is preheated. This translates to an increase in writing
speed.
The invention has been described in detail with particular reference to
preferred embodiments thereof, but it will be understood that variations
and modifications can be effected within the spirit and scope of the
invention.
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